"There will definitely be a huge cleanup, and there will be carpeted areas that will need to have carpet replaced."

NSW SES acting commissioner Jim Smith says there's been an 'amazing' amount of water that has passed through the school.

"It's devastating for the school but thankfully it was late at night when there was no one here so that was the one good part.

"Today we'll be working closely with Fire and Rescue NSW as they hose out the mud and debris at the school - that's a health issue so we want to get rid of that, then help the Deptartment of Education move on with getting the school back to normal."

He says last night the SES carried out 26 flood rescues in the Illawarra.